David Brown of the Washington Postwrites that the gel, tested on women in South Africa, reduced HIV infection risk by 39% in women who used it three quarters of the time they had sex. For those who used it 80% or more of the time, it reduced the risk by 54%. These numbers aren't perfect, but they're significant — many women around the world can't control condom use or sexual monogamy, the current main methods of reducing the spread of HIV. This is the first time a method just for women — that can potentially be used without a man knowing — has shown any effectiveness. Says AIDS researcher Bruce Walker, "We have never had any kind of tool that has effectively allowed women to protect themselves. This is really a game-changer."

The fact that the gel doesn't offer full protection could be an obstacle — will women use something consistently if they know it only works some of the time? Scientists may be able to fix the problem by altering the gel — they think a higher concentration of the drug tenofovir, which enters vaginal tissue to shield cells from HIV, may increase its effectiveness. And Brown also mentions the potential for making the gel "sexy" — perhaps it could be combined with lubricant and marketed as a sex aid as well as STD prevention (it provides some protection from herpes as well). Before that can happen, scientists need to test the gel on at least one more population of women, which could take several years. If they succeed, though, women will have a way to protect themselves that they alone control.